The GPIb-IX-V complex is a large multimeric protein complex on the platelet surface which consists of 4 different subunits GPIbα, GPIbβ, GPIX and GP V in the ratio of 2:2:2:1. Absence of some or all of the subunits of this complex results in a severe recessive bleeding disorder known as Bernard-Soulier syndrome (Blood (1998) 91(12):4397-4418). The GPlbα subunit contains the high affinity binding site for thrombin and the binding site for vWf. This complex has been implicated in the initial events associated with arterial thrombosis (Savage et al. (1996) Cell 84:289-297 and Weiss (1995) Thrombosis and Haemostasis 74(1):117-122).
It is known that GP V is a platelet and endothelial cell specific glycoprotein, and that it is a substrate for thrombin. It also is known that the activation of platelets by thrombin results in the loss of surface GP V. However, the precise role that GP V plays in the function of the GPIb-IX-V complex has not been described.